Acme::CPANModules::VersionNumber::Perl - Working with Perl version numbers (or version strings)


This document describes version 0.001 of Acme::CPANModules::VersionNumber::Perl (from Perl distribution Acme-CPANModules-VersionNumber-Perl), released on 2019-04-28.


Working with Perl version numbers (or version strings).

The core module version (a.k.a. should be your first go-to module when dealing with Perl version numbers. Other modules can also help in some aspects. Modules mentioned here include: Perl::Version, Versioning::Scheme::Perl.

Version numbers in Perl

There are two styles of version numbers used in the Perl world (i.e. for the versioning of perl interpreter itself and for versioning Perl modules): decimal (x.y) or dotted decimals (x.y.z or even more parts; the "v" prefix forces dotted decimal to avoid ambiguity when there is only a single dot, e.g. v1.2).

The former variant offers simplicity since version number can mostly be represented by a floating point number (quoting as string is still recommended to retain all precision and trailing zeros) and comparing versions can be done numerically. However they are often very limited so in those cases a dotted decimal variant can be used. For example the perl interpreter itself uses x.y.z convention.

Dotted decimal can be converted to decimal ("numified") form using this convention: minor and lesser parts are given (at least) three decimal digits each. For example, 1.2.3 becomes 1.002003. 1.20.3 becomes 1.020003. This can give some surprise which has bitten Perl programmers, novice and expert alike. In fact, it is the major gotcha when dealing with version numbers in Perl. For example '0.02' (a decimal form) numifies to 0.02, but 'v0.02' (a dotted decimal form) numifies to 0.002. Hence, v0.02 is less than 0.02 or even 0.01 when compared using version->parse(). Another gotcha is when a module author decides to go from 0.02 to 0.2.1 or 0.02.1. 0.02 (a decimal form) numifies to 0.02 while 0.2.1 or 0.02.1 (dotted decimal) numifies to 0.002001. Hence, going from 0.02 to 0.02.1 will actually decrease your version number. I recommend using x.yyy if you use decimal form, i.e. start from 0.001 and not 0.01. It will support you going smoothly to dotted decimal if you decide to do it one day.

The numification is also problematic when a number part is > 999, e.g. 1.2.1234. This breaks version comparison when comparison is done with version->parse().

Aside from the abovementioned two styles, there is another: CPAN distributions/modules can add an underscore in the last part of the version number to signify alpha/dev/trial release, e.g. 1.2.3_01. PAUSE will not index such releases, so testers will need to specify an explicit version number to install, e.g. cpanm Foo@1.2.3_01. In some cases you need to pay attention when comparing this kind of version numbers.

Checking if a string is a valid version number

To check if a string is a valid Perl version number, you can do:


which will die if $str contains an invalid version string. can handle the "v" prefix, (e.g. "v1.2"), dotted-decimal (e.g. "1.2.3" but also ""), as well as alpha/dev/trial part (e.g. "v1.1.1_001").

Parsing a version number

version->parse, obviously enough, is used to parse a version number string into a structure:

 use Data::Dump;
 dd( version->parse("1.2.3") );

which prints:

 bless({ original => "1.2.3", qv => 1, version => [1, 2, 3] }, "version")


 dd( version->parse("1.2.3_01") );


 bless({ alpha => 1, original => "1.2.3_01", qv => 1, version => [1, 2, 301] }, "version")

Comparing version numbers

You can compare two version numbers again using version->parse():

 version->parse($str1) <=> version->parse($str2)

For example:

 version->parse("1.2.3") <=> version->parse("v1.3.0");  # => -1

Be careful when dealing with alpha/dev/trial version:

 version->parse("1.2.3_01") <=> version->parse("v1.2.4")  ;  # => 1
 version->parse("1.2.3_01") <=> version->parse("v1.2.301");  # => 0
 version->parse("1.2.3_01") <=> version->parse("v1.2.400");  # => -1

Normalizing a version number

To normalize a version number:


This will add a "v" prefix, force a dotted decimal form, and remove insignifcant zeros. Examples:

 version->parse(1.2)      ->normal; # => "v1.200.0"
 version->parse("1.2.3")  ->normal; # => "v1.2.3"
 version->parse("1.2.30") ->normal; # => "v1.2.30"
 version->parse("1.2.030")->normal; # => "v1.2.30"

Incrementing a version number

Some modules like Perl::Version and Versioning::Scheme::Perl can help increase version numbers (or whichever part of the number). The last one can also decrement parts.



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